This invention relates to the field of cryogenic fluid transfer conduits and more particularly to cryogenic fluid transfer conduits used for cooling electronic integrated circuit packages.
Cryogenic fluids, such as liquid nitrogen (LN.sub.2), are known in the electrical arts both to lower the resistance of electrical conductors, and to remove "waste" heat generated by the passage of electrical current through materials which have resistance. For both purposes, cryogenic fluids are now being used to cool VLSI integrated circuits in computer applications. The reduction of resistance as a function of temperature means that some logic circuits increase in switching speed as the temperature of the integrated circuitry decreases. Moreover, the use of cryogenic fluids for the removal of "waste" heat permits the use of very high gate densities without unwanted temperature increases. Higher gate densities decrease the transit delay times between gates and further improve the switching times. Thus, the application of cryogenic fluids to computer VLSI circuits has important advantages.
Unfortunately, the devices known from existing patents for the application and transport of a cryogenic fluid to electrical and/or electronic hardware are inappropriate for the application and transport of a cryogenic fluid to general purpose, VLSI computer circuits. For example, U.S. Pat. No. 4,027,728 issued June 7, 1977, describes a non-cryogenic fluid cooling system which is too big and bulky to mount inside a computer cabinet. In addition to the problem associated with the physical size limitations, at cryogenic temperatures the transport conduits to and from the cooling chamber would soon be covered with liquid or frozen condensed water vapor. This is a significant problem because water within a computer cabinet can cause corrosion and/or unwanted signal coupling, both of which are unacceptable. Therefore, the use of a device according to this patent within a VLSI computer system is not desirable.
U.S. Pat. Nos. 3,162,716 issued Dec. 22, 1964, and 3,463,869 issued Aug. 26, 1969, describe systems which use cryogenic cooling. Included in each of these systems is a type of counter flow for better utilization of the cryogenic fluid. The differences, however, between the technology of the power distribution field from which these two patents are taken and the technology of the computer field are so great that only general background information about cryogenic cooling is provided. Information which is not readily adaptable to the field of VLSI computers. For example, the cryogenic fluid transfer conduit in each of the above referenced patents is manufactured out of metallic components, which tend, because of a good thermal conductance, to collect condensation either as liquid water or as ice crystals. The good thermal conductance is also accompanied by a good electrical conductance which can cause electrical short circuits unless strict observance to operating and maintenance procedures are adhered to. Moreover, a metallic conduit in a computer system tends to act as an antenna which could introduce unwanted signals into the system and also couple parasitic signals from inside the computer system to the outside environment. For these reasons, the two above mentioned patents from the electric power field do not disclose a cryogenic fluid transfer conduit which could be used or adapted for use with VLSI computer circuits within a typical electronic enclosure.
The use of a stainless steel, vacuum insulated conduit has been applied in the laboratory to prototypes of cryogenic, VLSI computer circuits, with less than ideal results. The stainless steel, vacuum insulated conduit is very rigid because it is composed of two concentric steel cylinders that are welded together at each end in order to seal in the vacuum. Such construction requires the vacuum conduit to be pre-formed during manufacture to the exact size and shape to fit within the computer enclosure. Even with a careful manufacturing process, the seals formed are not perfect and to maintain a good insulating vacuum, periodic removal for re-evacuation and resealing is necessary.
Stainless steel, vacuum insulated conduit is costly because of the expense of the stainless steel material, and because of the expense of the shaping procedures. Both expenses contribute to a high manufacturing cost. Additionally, because it is metallic, a stainless steel, vacuum insulated conduit also has the aforementioned problems of providing possible short circuit paths, as well as, conducting parasitic noise into and out of the internal regions of the computer system. Further, because at each end of the stainless steel, vacuum insulated conduit there is a metal-to-metal seal which is required to maintain the thermally insulating vacuum, each end is also is a thermally high conducting region which is not vacuum insulated. This region, at each end, typically collects ice and/or dripping condensation when operated in typical room temperature and humidity conditions.
It is an object of this invention to provide a cryogenic fluid conduit suitable for application within an electronics cabinet which does not collect ice or drip water anywhere along its extent.
It is another object of this invention to provide a small and flexible cryogenic fluid transfer conduit which can be readily cut to length.
It is a further object of this invention to provide a cryogenic fluid transfer conduit which is electrically non-conducting to prevent possible short circuits, and the transfer of parasitic noise either into or out of an electronics cabinet.
It is a further object of this invention to provide a cryogenic fluid transfer conduit which is inexpensive.